<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        * {
            padding: 0;
            margin: 0;
        }

        .wrap {
            width: 300px;
            margin: 100px auto 0;
        }

        table {
            border-collapse: collapse;
            border-spacing: 0;
            border: 1px solid #c0c0c0;
            width: 300px;
        }

        th,
        td {
            border: 1px solid #d0d0d0;
            color: #404060;
            padding: 10px;
        }

        th {
            background-color: #09c;
            font: bold 16px "微软雅黑";
            color: #fff;
        }

        td {
            font: 14px "微软雅黑";
        }

        tbody tr {
            background-color: #f0f0f0;
        }

        tbody tr:hover {
            cursor: pointer;
            background-color: #fafafa;
        }
    </style>

</head>

<body>
    <div class="wrap">
        <table>
            <thead>
                <tr>
                    <th>
                        <input type="checkbox" id="j_cbAll" />
                    </th>
                    <th>商品</th>
                    <th>价钱</th>
                </tr>
            </thead>
            <tbody id="j_tb">
                <tr>
                    <td>
                        <input type="checkbox" />
                    </td>
                    <td>iPhone8</td>
                    <td>8000</td>
                </tr>
                <tr>
                    <td>
                        <input type="checkbox" />
                    </td>
                    <td>iPad Pro</td>
                    <td>5000</td>
                </tr>
                <tr>
                    <td>
                        <input type="checkbox" />
                    </td>
                    <td>iPad Air</td>
                    <td>2000</td>
                </tr>
                <tr>
                    <td>
                        <input type="checkbox" />
                    </td>
                    <td>Apple Watch</td>
                    <td>2000</td>
                </tr>
                <tr>
                    <td>
                        总计
                    </td>
                    <td id="sum" colspan="2" style="text-align: center;color: red;">0.00</td>
                </tr>
            </tbody>
        </table>
    </div>
    <script>

        // 获取元素
        var j_cbAll = document.querySelector('#j_cbAll')
        var sumTd = document.querySelector('#sum')
        var j_tb = document.querySelector('#j_tb').querySelectorAll('input')
        // 当全选框选中，所有复选框都选中
        j_cbAll.addEventListener('click', function () {
            for (var i = 0; i < j_tb.length; i++) {
                j_tb[i].checked = j_cbAll.checked

            }
            var sum = getSum()
            sumTd.innerHTML = sum
        })



        // 给所有的复选框添加点击事件
        for (var i = 0; i < j_tb.length; i++) {

            j_tb[i].addEventListener('click', function () {
                var flag = true;
                for (var i = 0; i < j_tb.length; i++) {
                    if (!j_tb[i].checked) {
                       flag = false;
                        break;
                    }

                }
                j_cbAll.checked = flag;
                var sum = getSum()
                sumTd.innerHTML = sum

            })

        }

        // 求和函数公式
        function getSum() {
            // 获取所有的已选复选框
            var checks = document.querySelectorAll('#j_tb input:checked')
            var sum = 0;
            // 复选框的爸爸的爸爸是tr
            // 要获取的是tr的最后一个孩子的值
            for (var i = 0; i < checks.length; i++) {
                var tr = checks[i].parentNode.parentNode
                var num = +tr.children[tr.children.length - 1].innerHTML
                sum = sum + num
            }
            return sum
        }






    </script>


</body>

</html>